1. Field of the Invention
The present invention relates to a recording medium, a host device accessing the recording medium, and a data processing method between a recording medium and a host device. More particularly, the invention relates to error check processing when the host device mounts a recording medium which is a semiconductor recording medium.
2. Related Art
The recording medium for recording digital data such as music contents, moving picture contents and still picture contents is available in various types including semiconductor recording medium, magnetic disk, optical disk, and magneto-optical disk. Among them, the semiconductor recording medium can be reduced in size and weight, and thus it is widely used recently mainly in portable appliances such as digital still camera and mobile telephone terminal. Representative examples of semiconductor recording medium include SD Memory Card (registered trademark), Memory Stick (registered trademark), and Compact Flash (registered trademark). These semiconductor recording media tend to increase in capacity by doubles every year.
Digital data stored in recording region of the semiconductor recording medium is managed by a file system. A file system manages the recording region by dividing it into sectors which are minimum access units and clusters which are sets of sectors, and manages one or more clusters as file.
One of the existing file systems is FAT file system (see non-patent document 1). FAT file system is generally used in personal computers (PCs) and other information appliances, and is also a principal file system in the semiconductor recording medium. In a file system, generally, as the capacity of the recording region increases, the information required for its management (hereinafter called “file system management information”) also increases.
A host device of the semiconductor recording medium such as portable appliance performs mounting process, as prior process for processing digital data stored in the recording region of the semiconductor recording medium. In the mounting process, specifically, the file system management information is read and analyzed, and errors in the read file system management information are checked.
If abnormality is found in the file system management information, the host device must execute error handling or error correction properly. Otherwise, fatal troubles such as the followings may occur. The digital data recorded in the semiconductor recording medium is abandoned in irreparable state by the host device, the digital data recorded by one host device may not be normally reproduced by the other host device, and so on. Hence, for the host device executing write process, error check of the file system management information is an indispensable process.
However, due to increase of the file system management information as a result of enlarged capacity, the error checking time increases more and more in the mounting process in the host device. Hence, the user has to wait always for a specific time before use of recording medium, and the convenience is lowered.
The same problem also occurs when the number of error check items is increased for the purpose of enhancing the reliability.
Hitherto, to solve this problem, the following method has been proposed (for example, see patent document 1).
In patent document 1, an “open flag” showing whether the host device is using the semiconductor recording medium or not is stored in the recording region of the recording medium. This open flag is set to ON when the host device starts a series of write process, and set to OFF when the file system management information achieves consistency after completion of series of write process. This open flag shows presence or absence of consistency of data stored in the semiconductor recording medium with the file system.
When mounting the semiconductor recording medium, the host device refers to the open flag. It is judged that the series of write process is interrupted in the midst of the process, when the flag is ON. It is judged that the series of write process is normally finished, when the flag is OFF. Thus, patent document 1 presents a method of simplifying judgment as to whether the file system management information requires a correction or not by referring to the open flag.
Patent document 1: JP 05-12092 A
Non-patent document 1: ISO/IEC 9293, “Information Technology—Volume and file structure of disk cartridges for information,” 1994
However, the prior art has the following problems.
That is, in patent document 1, since the open flag is provided in the recording region which can be freely read and written by any host device, it must be guaranteed that all host devices writing in the recording region must process the open flag correctly. Otherwise, the open flag of OFF does not always indicate that the file system management information achieves consistency.
More specifically, in the recording medium of patent document 1, the open flag is updated by direct instruction from the host device. In other words, the open flag is turned on or off by a command or direct writing from the host device. When data is recorded in the semiconductor recording medium having an open flag, by a host device not having function of processing an open flag, and if finished abnormally, the open flag is, OFF (showing presence of consistency) although the data and file system are not consistent. Afterwards, in such a recording medium, when a host device having an open flag processing function processes based on this false open flag, an operation trouble may occur.
Thus, in the method of patent document 1, if the recording medium having open flag is once accessed by a host device not applicable to an open flag, the reliability of an open flag may be spoiled. Hence, there is a problem that data cannot be exchanged between a conventional host device not having an open flag processing function and a new host device applicable to an open flag, by using a semiconductor medium having the open flag.